Eight million people die each year from cancer worldwide. Cancer is the second cause of death in the United States and in Europe. For many solid tumors, in spite of the reduction of the carcinoma by surgery and first-line chemotherapy, resistance to the drugs causing the death of patients is developed. This phenomenon of resistance to chemotherapeutic agents is a real public health problem.
The Hedgehog (Hh) signaling pathway controls cell differentiation and proliferation. It plays a crucial role during embryonic development and, in adulthood, in stem cell homeostasis and tissue regeneration. However, Hh signaling is also involved in cancer development, progression, and metastasis. Indeed, aberrant activation of the Hh signaling has been identified in many aggressive cancers such as breast cancer, lung cancer, colorectal cancer, ovarian cancer, pancreatic cancer, melanoma or multiple myeloma (Varjosalo and Taipale 2008; Scales and de Sauvage, 2009), in particular in cells exhibiting resistance to chemotherapeutic agents such as cancer stem cells or tumor initiating cells. Recently, Yue et al. (2014) showed that Hh signaling is involved in lung squamous cell carcinomas (SCC) recurrence, metastasis and resistance to chemotherapy. Several studies have shown that antagonizing the Hh signaling receptor Smoothened (Smo) could provide a way to interfere with tumorigenesis and tumor progression. The most commonly used antagonist of the Hh pathway is the plant alkaloid cyclopamine (Taipale et al. 2000). Genentech has a long lasting research project on Hh pathway and has identified a new drug for basal-cell carcinoma treatment. Vismodegib is a first-in-class investigational, oral medicine that is designed to selectively inhibit Hh signaling by targeting Smo (Garber, 2008 Scales and de Sauvage, 2009). It has been reported that autocrine expression of Hh morphogenes such as Sonic Hedgehog (Shh) is required for growth of some cancers (Dahmane et al., 1997; Karhadkar et al., 2004), and stromal cell-derived Shh can also activate the Hh pathway in tumors (Becher et al., 2008). One Shh-specific monoclonal antibody (5E1) has been shown to block the growth of some tumors, including small-cell lung carcinoma (Watkins et al., 2003). In addition to targeting tumors that have hyperactive Hh pathway themselves, antagonists of the Hh pathway could also affect growth of tumors that use Hh ligands to induce angiogenesis (Pola et al., 2001; Nagase et al., 2008) or recruit other types of stromal cells supporting tumor growth. Because adults can tolerate inhibition of the Hh pathway (Berman et al., 2002; Kimura et al., 2008), specifically blocking Hh signaling offers an effective treatment for the various cancers originating from aberrant Hh pathway activation. However, systemic treatment of pediatric tumors such as medulloblastoma may not be feasible due to the severe effects that transient inhibition of the Hh pathway has on bone growth (Kimura et al., 2008).
Two different genes (Patched 1 and Patched 2) encode homologues of Drosophila Patched, the Hh morphogen receptor. Mice deficient in Patched 2 are viable, but develop alopecia and epidermal hypoplasia and have increased tumor incidence in the presence of one mutant allele of Patched 1. Loss of Patched 1, in turn, results in complete activation of the Hh pathway, suggesting that Patched 1 is the functional ortholog of Drosophila Patched (Varjosalo and Taipale, 2008). Patched 1, referred to as Patched, whose expression is induced upon activation of the Hh pathway, is overexpressed in many cancers: lung, breast, basal cells of the skin, prostate, colon, brain (Scales and de Sauvage, 2009; Blotta et al., 2012; Jeng et al., 2014) and myeloid leukemia (Zhao et al., 2009; Queiroz et al., 2010). Recent studies suggest Patched as an early marker of gastric and thyroid cancers (Saze Z et al., 2012; Xu X et al., 2012). As already described, in some cancers, the morphogen Hh is overproduced by cancer cells themselves and activates Hh signaling by interacting with its receptor Patched. Nakamura and co-workers showed in 2007 that the use of an antibody directed against one of the extracellular domains of Patched involved in the interaction with Hh inhibits proliferation of pancreatic cancer cells. In 2012, they showed that three peptides from Hh involved in interaction with Patched could suppress the proliferation of two pancreatic cancer cell lines and decrease the expression of the transcription factor Glil both in vitro and in vivo (Nakamura et al., 2012).
Inventors discovered that the Hh receptor Patched has a drug efflux activity and can contribute to the resistance of cancer cells to chemotherapeutic agents (Bidet et al., 2012; patent WO2012/080630). Indeed, they have shown that the human Patched protein expressed in yeast confers resistance to various chemotherapeutic agents used to treat many metastatic cancers (doxorubicin, methotrexate, temozolomide, 5-FU) and effluxes doxorubicin. This yeast model has been extended to fibroblasts (often used for the study of the Hh pathway) and human cancer cell lines overexpressing Patched such as melanoma and Leukemia cell lines. These cells release (efflux) less doxorubicin in the presence of the Patched ligand Hh, which induces Patched internalization and degradation. Viability tests carried out with these different cell lines showed that the presence of Hh increases the cytotoxicity of doxorubicin. These results suggest that the Hh receptor Patched can participate in the phenomenon of resistance to chemotherapeutic agents of cancer cells and allowed to propose Patched as a new target for anti-cancer therapy (patent WO2012/080630) (FIG. 1).
Currently, no antagonist of Patched is available. There is thus a need for compounds able to inhibit the drugs efflux activity of the Patched receptor and which may be used in cancer therapy.